The conventional process of opening a hot water valve and running a water stream to “warm up the water” generally means sending water that is too cold down the waste drain, e.g., because water in a hot water line has cooled-down in the hot-water pipe (i.e., between the water heater and the point of use). This wasted resource, previously heated potable water, is normally purged from the system with no benefit received.
Users often find that manual control of water temperature and output flow rate in showers and sinks can be difficult to operate with consistency. This can create an unsatisfactory or annoying situation when attempting to achieve a desired setting and maintain that setting. For example, small valve adjustments may result in large temperature and flow rate responses, with resultant waste of water, time, and thermal energy. Achieving a successful temperature adjustment on one day is no guarantee against experiencing a different outcome on another occasion. That is, adjusting to the same setting may suddenly result in scalding water or freezing cold water, creating a moment of distraction, inconvenience or discomfort on another day. Another issue which arises in shower systems is that when there is a sudden pressure drop (e.g., due to flushing of a toilet), there may be an abrupt loss of water pressure in a cold water supply line, which may dramatically shift the mix of hot/cold water and even cause a user to experience scalding hot shower water.